Background and Basis of Presentation (Share Repurchase Table) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Repurchase of common stock (shares)	14.4	2.7	22.1	5.5
Aggregate cost of shares repurchased	$ 1,049	$ 173	$ 1,600	$ 341	$ 1,030
Average price of repurchased shares, per share (usd per share)	$ 72.85	$ 64.06	$ 72.47	$ 61.90